Computer disc drives are dynamic magnetic storage units having high bit densities. They are very high precision units requiring close dimensional tolerances in manufacturing and are complex and delicate mechanically. Rotary disc drives generally comprise rotatable memory discs, transducer heads and a pivotally mounted, magnetically driven, actuator arm assembly supporting the transducer heads for bidirectional movement along an arcuate path over the discs.
Conventionally, the pivotally mounted actuator arm carries the flexure assemblies which mount the magnetic heads. The actuator arm is pivotally mounted in an actuator housing by means of a shaft assembly. Very precise control of the axial and radial stiffness and location of this shaft assembly is required for the servo system and the servo system electronics to work properly, and for heads to maintain position with respect to each other and the rest of the structure, particularly the data tracks on the memory discs. The bearings must have a precisely controlled axial and radial preload to do this. Helical compression springs have been used to provide these preloads in prior art structures. One helical spring is used to provide the axial preload on the bearings of the shaft assembly. A second helical spring, disposed radially at one of the bearings in which the shaft is journaled, is used to provide a radial or side load if required, to that bearing. The use of a radially disposed helical spring requires an additional machining operation on the actuator housing in a position off the main axis. The main axis is the axis about which the actuator arm is pivoted. Thus machine operations for installing the radially disposed helical spring cannot easily be performed in the same fixtures used in machining the bores in which the bearings of the shaft assembly for the actuator arm are positioned. This increases manufacturing costs.